1. Field of the Invention
The present invention relates to a vehicle surroundings monitoring device mounted on a vehicle and used for monitoring of surroundings around the vehicle and, more particularly, to a vehicle surroundings monitoring device for alarming a driver to enable the driver to avoid contact with or collision against an obstacle particularly at the time of lane change or the like.
The entire content of the basic Japanese Patent Application from which the priority under the Convention is claimed in this application is hereby incorporated by reference into this application.
2. Description of the Related Art
The inventors of the present invention have already filed an application of a vehicle surroundings monitoring device of this kind in Japanese Patent Application No. Hei 11-325688. This vehicle surroundings monitoring device has a transmitting circuit for generating waves to be transmitted, an antenna mounted in the vicinity of or in a door mirror assembly of a vehicle and capable of radiating transmitted waves through a mirror surface of the door mirror, and a receiving circuit for receiving, by the antenna, reflected waves from an object existing near the vehicle, the reflected waves propagating to the antenna through the mirror surface of the door mirror. This vehicle surroundings monitoring device is characterized by having a reflective film which is formed on the mirror surface of the door mirror by vapor deposition, and which reflects light of wavelengths in the visible region but allows electric waves of several gigahertz to pass therethrough.
In such a vehicle surroundings monitoring device, however, even if a reflective film capable of transmitting of electric waves is vapor-deposited on the mirror surface of the door mirror as described above, the surface of the mirror base and the reflective film can partially reflect electric waves which should be passed through the mirror. This reflection causes straying of electric waves radiated from the transmitting antenna, such that some of the electric waves propagate to the receiving antenna without being reflected by any external obstacle. In such a situation, the monitoring device may operate as if an obstacle always exists at a short distance from the vehicle. When an object exists actually at a short distance from the vehicle, the monitoring device cannot detect the object if the distance resolution of the radar is not sufficiently high. Also, the distance measuring performance may be influenced by the above-described unwanted reflection to such an extent that the possibility of detection failure or a false alarm is high.
There is also a possibility of the mirror in the door mirror assembly being broken by contact with the antenna incorporated in the door mirror assembly.
In view of the above-described problem, an object of the present invention is to provide a vehicle surroundings monitoring device capable of performing distance measurement as desired even in a short-distance range to provide unerring alarm information to a driver.
Another object of the present invention is to provide a vehicle surroundings monitoring device capable of preventing a mirror in a door mirror assembly from being broken by contact with an antenna incorporated in the door mirror assembly.
To achieve the above-described objects, according to one aspect of the present invention, there is provided a vehicle surroundings monitoring device which monitors surroundings around a vehicle, the device is characterized by comprising a transmitting antenna mounted in a door mirror assembly of the vehicle, the transmitting antenna for radiating transmitted waves through a mirror surface of a door mirror in the door mirror assembly, a receiving antenna mounted in the door mirror assembly, the receiving antenna for receiving, through the mirror surface of the door mirror, reflected waves from an object existing in the surroundings of the vehicle, and a stray electric wave limiting member for reducing electric wave components straying from the transmitting antenna into the receiving antenna.
Specifically, the above-described stray electric wave limiting member is characterized by comprising an electric wave absorbing member provided between opening surfaces of the door mirror corresponding respectively to the transmitting antenna and the receiving antenna.
Also, the above-described stray electric wave limiting member is characterized by comprising a metal plate provided between the transmitting antenna and the receiving antenna.
Also, the above-described stray electric wave limiting member is characterized by comprising an electric wave absorbing member provided between the transmitting and receiving antennas and the door mirror except in front of the opening surfaces of the door mirror corresponding to the transmitting and receiving antennas.
Also, the above-described stray electric wave limiting member is characterized by comprising a matching layer provided between the transmitting and receiving antennas and the door mirror.
According to another aspect of the present invention, there is provided a vehicle surroundings monitoring device which monitors surroundings around a vehicle, the device is characterized by comprising a transmitting antenna mounted in a door mirror assembly of the vehicle, the transmitting antenna for radiating transmitted waves through a mirror surface of a door mirror in the door mirror assembly, a receiving antenna mounted in the door mirror assembly, the receiving antenna for receiving, through the mirror surface of the door mirror, reflected waves from an object existing near the vehicle, and a cushioning member provided between the transmitting and receiving antennas and the door mirror.
In a vehicle surroundings monitoring device according to the present invention, a stray electric wave limiting member for reducing electric wave components straying from transmitting antenna into the receiving antenna is provided to reduce electronic wave components straying from the transmitting antenna into the receiving antenna inside a door mirror, thereby ensuring a desired distance measuring performance in a short-distance range to provide unerring alarm information to a driver.
Also, a cushioning member is provided between the transmitting and receiving antennas and the door mirror to prevent a mirror in the door mirror from contacting and breaking the door mirror.